Optical interconnection for holographic memories and method for using the same

Abstract

An optical interface of a holographic memory system electrically selects one of several optical pathways to store or retrieve an image from a holographic memory by activating liquid crystal polarization rotators and novel liquid crystal gratings. In a preferred embodiment a spatial light modulator, a pixelized readout device (i.e., focal-plane array), a series of polarizing optical components, liquid-crystal polarization rotators, liquid-crystal beam-steering devices, and interconnecting and imaging optics are provided. The parallel interconnection accepts a laser-beam input, divides the beam among multiple paths, imparts a data-bearing spatial signature on a signal beam by means of a spatial light modulator, steers a reference beam by means of liquid-crystal beam-steering devices, and directs the appropriate beams into the recording medium. The interconnection functions are realized within a solid-optical assembly requiring no air-glass interfaces, and the beam-steering functions for the reference beam are accomplished by non-mechanical means using liquid-crystal devices.

We claim:  
     
       1. An optical memory system comprising: 
       input means for receiving light encoded with data;  
       holographic storage means coupled to said input means for receiving and storing said light encoded with data in a multiplexed three dimensional optical memory at one of a plurality of defined angles, and outputting said light encoded with data as light output;  
       output means coupled to the holographic storage means for receiving said light encoded with data and passing said light encoded with data to an external device;  
       a plurality of optical paths, each associated with at least one of said plurality of defined angles of the holographic storage means, and each coupling said input means to said holographic storage means;  
       electrically controlled non-moving optical switching means coupled to said plurality of optical paths for selecting and activating any one of said plurality of optical paths to pass light to said holographic storage means at the defined angle associated with that path for storing or retrieving data; and  
       control means, coupled to said electrically controlled non-moving optical switching means for receiving an external input defining a desired holographic memory location, and for selectively activating said electrically controlled non-moving optical switching means to select one of said plurality of optical paths associated with said desired holographic memory location,  
       wherein said electrically controlled non-moving optical switching means comprises at least one liquid crystal cell, selectively actuated to selectively polarize the light encoded with data and transmit portion of the light encoded with data through as a reference beam over a corresponding one of the plurality of optical paths.  
     
     
       2. The optical memory system of claim  1 , wherein said plurality of optical paths further comprise interconnection elements optically interconnecting said input means with said holographic storage means, 
       wherein said interconnection elements comprise a solid-optical assembly having no air-glass interfaces.  
     
     
       3. An optical memory system comprising: 
       input means for receiving light encoded with data;  
       holographic storage means coupled to said input means for receiving and storing said light encoded with data in a multiplexed three dimensional optical memory at one of a plurality of defined angles, and outputting said light encoded with data as light output;  
       output means coupled to the holographic storage means for receiving said light encoded with data and passing said light encoded with data to an external device;  
       a plurality of optical paths, each associated with at least one of said plurality of defined angles of the holographic storage means, and each coupling said input means to said holographic storage means;  
       electrically controlled non-moving optical switching means coupled to said plurality of optical paths for selecting and activating any one of said plurality of optical paths to pass light to said holographic storage means at the defined angle associated with that path for storing or retrieving data; and  
       control means, coupled to said electrically controlled non-moving optical switching means for receiving an external input defining a desired holographic memory location, and for selectively activating said electrically controlled non-moving optical switching means to select one of said plurality of optical paths associated with said desired holographic memory location,  
       wherein said electronically controllable non-moving optical switching means comprises:  
       a polarizing beam-splitter cube; and  
       a liquid crystal polarization rotator, coupled to the beam-splitter cube,  
       wherein said liquid crystal polarization rotator may be selectively engagable to direct a light beam through the polarizing bean-splitter cube to a selected one of the plurality of optical paths.  
     
     
       4. An optical memory system comprising: 
       input means for receiving light encoded with data;  
       holographic storage means coupled to said input means for receiving and storing said light encoded with data in a multiplexed three dimensional optical memory at one of a plurality of defined angles, and outputting said light encoded with data as light output;  
       output means coupled to the holographic storage means for receiving said light encoded with data and passing said light encoded with data to an external device;  
       a plurality of optical paths, each associated with at least one of said plurality of defined angles of the holographic storage means, and each coupling said input means to said holographic storage means;  
       electrically controlled non-moving optical switching means coupled to said plurality of optical paths for selecting and activating any one of said plurality of optical paths to pass light to said holographic storage means at the defined angle associated with that path for storing or retrieving data; and  
       control means, coupled to said electrically controlled non-moving optical switching means for receiving an external input defining a desired holographic memory location, and for selectively activating said electrically controlled non-moving optical switching means to select one of said plurality of optical paths associated with said desired holographic memory location,  
       wherein said plurality of optical paths further comprise interconnection elements optically interconnecting said input means with said holographic storage means,  
       wherein said interconnection elements comprise a solid-optical assembly having no air-glass interfaces.  
     
     
       5. An optical memory system comprising: 
       at least one electrically controlled non-moving optical switching means for selectively diverting at least a portion of an input light beam as a reference beam;  
       a holographic recording medium, coupled to said at least one electrically controlled non-moving optical switching means, for receiving another portion of the input beam as a signal beam;  
       at least one reference beam path, coupled to the at least one electrically controlled non-moving optical switching means and the holographic recording medium, each of the at least one reference beam path diverting a corresponding reference beam to the holographic recording medium at a corresponding fixed predetermined angle; and  
       interconnection elements optically interconnecting said at least one electrically controlled non-moving, optical switching means, said spatial light modulator, and said holographic recording medium,  
       wherein said interconnection elements comprise at least one solid-optical assembly having no air-glass interfaces.  
     
     
       6. An optical memory system comprising: 
       at least one electrically controlled non-moving optical switching means for selectively diverting at least a portion of an input light beam as a reference beam;  
       a holographic recording medium coupled to said at least one electrically controlled non-moving optical switching means, for receiving another portion of the input beam as a signal beam;  
       at least one reference beam path, coupled to the at least one electrically controlled non-moving optical switching means and the holographic recording medium, each of the at least one reference beam path diverting a corresponding reference beam to the holographic recording medium at a corresponding fixed predetermined angle;  
       a spatial light modulator, coupled to the at least one electrically controlled non-moving optical switching means and the holographic recording medium, for receiving the signal beam and imparting a data-bearing spatial signature on a signal beam, and for passing the signal beam imparted as with a data-bearing spatial signature to the holographic recording medium; and  
       interconnection elements optically interconnecting said at least one electrically controlled non-moving optical switching means, said spatial light modulator, and said holographic recording medium,  
       wherein said interconnection elements comprise at least one solid-optical assemble having no air-glass interfaces.  
     
     
       7. An optical memory system comprising: 
       at least one electrically controlled non-moving optical switching means for selectively diverting at least a portion of an input light beam as a reference beam;  
       a holographic recording medium, coupled to said at least one electrically controlled non-moving optical switching means, for receiving another portion of the input beam as a signal beam; and  
       at least one reference beam path, coupled to the at least one electrically controlled non-moving optical switching means and the holographic recording medium, each of the at least one reference beam path diverting a corresponding reference beam to the holographic recording medium at a corresponding fixed predetermined angle,  
       wherein said at least one electrically controlled non-moving optical switching means comprises at least one liquid-crystal device.  
     
     
       8. The apparatus of claim  7 , wherein the spatial light modulator comprises a transmissive spatial light modulator. 
     
     
       9. The apparatus of claim  8 , wherein the spatial light modulator comprises a reflective spatial light modulator. 
     
     
       10. A method of storing data in an optical memory system comprising: 
       selectively diverting at least a portion of an input light beam as a reference beam using at least one electrically controlled non-moving optical switch,  
       receiving, in a holographic recording medium coupled to the at least one electrically controlled non-moving optical switch, another portion of the input light beam as a signal beam, and  
       diverting, using at least one reference beam path coupled to the at least one electrically controlled non-moving optical switch and the holographic recording medium, a corresponding reference beam to the holographic recording medium at a corresponding fixed predetermined angle,  
       wherein said using at least one electrically controlled non-moving optical switch comprising at least one group of steps of:  
       (1) selectively actuating at least one liquid crystal device to selectively polarize said portion of the input light beam and to transmit said portion of the light beam through as a reference beam over a corresponding one of a plurality of optical paths;  
       (2) using a polarizing beam-splitter cube; and  
       using a liquid crystal polarization rotator coupled to the beam-splitter cube,  
       wherein said liquid crystal polarization rotator may be selectively engagable to direct a light beam through the polarizing beam-splitter cube to a selected one of a plurality of optical paths;  
       (3) optically interconnecting said electrically controlled non-moving optical switch with said holographic recording medium with at least one solid-optical assembly having no air-glass interfaces.  
     
     
       11. The method of claim  10 , further comprising the step of: 
       receiving the signal beam in a spatial light modulator coupled to the at least one electrically controlled non-moving optical switch and the holographic recording medium,  
       imparting a data-bearing spatial signature on a signal beam with the spatial light modulator, and  
       passing the signal beam imparted with a data-bearing spatial signature to the holographic recording medium.